As sensors for detecting acceleration, are known acceleration sensors, inertia sensors and the like. The present invention also covers semiconductor accelerometers with gyroscopic functions and angular acceleration measuring functions. Unless otherwise specified, the following description is made using the term “accelerometer/acceleration sensor” for a sensor for detecting acceleration.
FIGS. 1A-1D each show a widely practiced calibration method of an accelerometer/acceleration sensor. In terms of international standards, they are methods described in ISO 16063-11 or ISO 5347 Part 1. FIG. 2 shows a method of measuring transverse sensitivity described in ISO 5347 Part 11.
FIG. 1A shows a calibration method carried out by mounting a single-ended uniaxial acceleration sensor (accelerometer) 1 on a table 2a of a uniaxial vibration generator 2 for generating translational motion (the table 2a vibrates in the direction of the two-directional arrow in FIG. 1A with respect to the body 2b), by measuring the motion of the table with a laser interferometer (not shown) with aligning the motion direction of the uniaxial vibration generator 2 with the sensing axis of the uniaxial acceleration sensor 1, and by comparing measured results by the laser interferometer with the output of the acceleration sensor 1. It functions as a primary calibration method. The term “single-ended accelerometer” refers to an accelerometer with only one mounting surface. On the other hand, the term “double-ended accelerometer” refers to an accelerometer for calibration, which has two mounting surfaces and can undergo back-to-back coupling.
FIG. 1B shows a calibration method carried out by mounting a double-ended uniaxial acceleration sensor (accelerometer) 3 on the table of the uniaxial vibration generator 2, by measuring the motion of the table with the laser interferometer with aligning the motion direction of the uniaxial vibration generator with the sensing axis of the uniaxial acceleration sensor 3, and by comparing measured results by the laser interferometer with the output of the acceleration sensor 3. It also functions as a primary calibration method.
FIG. 1C shows a calibration method carried out by coupling the double-ended reference acceleration sensor 3 calibrated by the method of FIG. 1B and the calibration target acceleration sensor 1 in series with aligning their sensitivity axes, by moving them with aligning their sensitivity axes with the motion direction of the vibration generator, and by comparing the output of the reference accelerometer 3 with the output of the calibration target accelerometer 1. It functions as a secondary calibration method.
FIG. 1D shows a primary calibration method of an angular acceleration detecting acceleration sensor corresponding to the method shown in FIG. 1A. The reference numeral 25 designates a uniaxial vibration generator for generating vibration angular acceleration. A disk-shaped table 25a carries out rotational vibration in the directions of the two-directional arrow in FIG. 1D with respect to the body 25b. An angular acceleration detecting acceleration sensor (angular acceleration sensor) 26 is mounted on the table 25a of the uniaxial vibration generator 25 for generating the vibration angular acceleration in such a manner that the central axis (the central axis agrees with the sensing axis) comes into the center of the table 25a and becomes perpendicular to the table 25a. The table 25a has an optical diffraction grating formed on its side. To measure the vibration angular acceleration of the table 25a, the optical diffraction grating on the outer edge of the table 25a is irradiated horizontally with the laser from the laser interferometer. The primary calibration is conducted by applying the vibration angular acceleration around the sensing axis of the angular acceleration sensor 26 by carrying out the rotational vibration of the table 25a, and by comparing the vibration angular acceleration detected from the changes in the reflected light of the laser radiating the optical diffraction grating of the table 25a with the output signal of the calibration target angular acceleration sensor 26. It is a method described in a standard being prepared now by ISO. The method enables the calibration of the reference angular acceleration sensor. Thus, it can function as the secondary calibration as the method shown in FIG. 1C by mounting the reference angular acceleration sensor and calibration target angular acceleration sensor on the uniaxial vibration generator for generating the vibration angular acceleration with aligning their axes. In the existing circumstances, no reference acceleration sensor for vibration angular acceleration exists. This is because its standard is yet to be completed, or no production is present which is experimentally demonstrated that it functions as a reference acceleration sensor for the vibration angular acceleration.
Next, a method will be described of obtaining the transverse sensitivity as shown in FIG. 2 and described in ISO 5347-11: 1993 “Methods for the calibration of vibration and shock pick-ups—Part 11: Testing of transverse sensitivity”.
On a plane normal to the sensing axis of the acceleration sensor 1 for detecting the translational acceleration, vibration acceleration A sin ωt is applied (indicated by the arrow 4 in FIG. 2). Normalizing the obtained sensitivity by the main axis sensitivity gives the transverse sensitivity. According to the ISO standard, the transverse sensitivity is obtained with varying, an angle θ (the angle between the direction of the vibration acceleration 4 and a marking 5 put to the reference position of the acceleration sensor 1 on the plane normal to the sensing axis of the acceleration sensor 1). Then it instructs to report the transverse sensitivity value and angle θman when the maximum value is obtained, and the transverse sensitivity value and angle θmin when the minimum value is obtained. In a word, the number of the transverse sensitivity parameters is one in the ISO 5347-11: 1993 “Methods for the calibration of vibration and shock pick-ups—Part 11: Testing of transverse sensitivity”.